Compressed air aspirating and propellant actuated fluid product dispenser

ABSTRACT

A compressed air aspirating and propellant actuated dispenser for dispensing fluid products. A valve assembly has a compressed air flow path therethrough with a valve member obturating the compressed air flow path. A product containing means in the device is connected to the aspirating means by a product flow path. A hollow enclosure surrounds the other end of the compressed air flow path and a piston is movable in the hollow enclosure toward the valve and engagable with the valve member after it has moved into the hollow enclosure for actuating the valve member for opening the compressed air flow path. An aerosol propellant cartridge having a spring loaded dispensing valve is mounted on the device for movement relative thereto for opening said dispensing valve, the dispensing valve being directed into the hollow enclosure for moving the piston into the hollow enclosure. When the device is moved relative to the cartridge, propellant dispensed into the hollow enclosure drives the piston to compress air in the hollow enclosure ahead of the piston and the piston engages the valve member after it has moved into the enclosure sufficiently far to build up the desired pressure of air within the enclosure in order to open the valve member to allow the compressed air to flow along the compressed air flow path. The propellant is then vented away from the point of product dispensing.

United States Patent 91 Thornton et al.

[ 1 COMPRESSED AIR ASPIRATING AND PROPELLANT ACTUATED FLUID PRODUCT DISPENSER [75] lnventors: Marvin L. Thornton, Candlewood Shores, Brookfield, Conn; Pasquale R. Riccio, Salem, NH.

[73] Assignee: Ciba-Geigy Corporation, Ardsley,

[22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,064

Related US. Application Data [63] Continuation-impart of Ser. No. 252,754, May 12,

[52] US. Cl. 222/193 [51] Int. Cl B65d 83/14 [58] Field of Search... 222/193, 389, 131, 183, 129;

[56] References Cited UNITED STATES PATENTS 3,408,010 10/1968 Fukui 239/308 3,733,010 5/1973 Riccio 222/193 Primary Examiner-Stanley H. Tollberg Attorney, Agent, or F irm-Wenderoth, Lind & Ponack [451 Jan. 29, 1974 [57] ABSTRACT A compressed air aspirating and propellant actuated dispenser for dispensing fluid products. A valve assembly has a compressed air flow path therethrough with a valve member obturating the compressed air flow path. A product containing means in the device is connected to the aspirating means by a product flow path. A hollow enclosure surrounds the other end of the compressed air flow path and a piston is movable in .the hollow enclosure toward the valve and engagable with the valve member after it has moved into the hollow enclosure for actuating the valve member for opening the compressed air flow path. An aerosol propellant cartridge having a spring loaded dispensing valve is mounted on the device for movement relative thereto for opening said dispensing valve, the dispensing valve being directed into the hollow enclosure for moving the piston into the hollow enclosure. When the device is moved relative to the cartridge, propellant dispensed into the hollow enclosure drives the piston to compress air in the hollow enclosure ahead of the piston and the piston engages the valve member after it has moved into the enclosure sufficiently far to build up the desired pressure of air within the enclosure in order to open the valve member to allow the compressed air to flow along the compressed air flow path, The propellant is then vented away from the point of product dispensing.

10 Claims, 7 Drawing Figures PATENIED JAN 2 9 I974 SHEET 1 OF 2 1v COMPRESSED AIR ASPIRATING AND PROPELLANT ACTUATED FLUID PRODUCT DISPENSER PRIORART There has recently been developed a type of dispenser for fluids which utilizes compressed air. for dispensing fluids in the form of a spray. This dispenser gradually builds up the pressure of air, and when a predetermined: pressure has been reached, the compressed air is released suddenly for aspirating the fluid product as a spray. 7

There are many advantages to such adispenser, among which is the fact that it is not necessary to mix a conventional aerosol type propellant, such as Freon, with the product to dispense it, whereby possible harm to users of the dispenser due to inhalation of the Freon propellant after it has been used to dispense the fluid is avoided. A further advantage is that such dispensers provide automatic metering of the fluid product to be dispensed, since only a certain quantity of air used to dispense the product iscompressed to a given pressure by the user of the dispenser for each dispensing action.

Such dispensers are disclosed in copending applica-' tions Ser. No. 44,694, now US. Pat. No. 3,672,545and Ser. No. 90,897, Nov. 11, I970, Ser. No. 139,027 Apr. 30, I971, and others.

In all of the various forms of the device as disclosed in the previously filed applications, the piston means for compressing the air, which moves relative to the elongated body of the device or elongated body which moves relative to the piston means, is moved by direct force produced by the fingers of the user. While this is satisfactory for many uses, it often occurs that the particular product'or the amount of a product to be dispensed by the device requires more air or air at a means can be actuated to operate the air compression means by simplefinger pressure of the user.

These objects are achieved by the provision of a fluid product dispenser comprising a valve assembly having an elongated valve body which has a compressed air flow path therethrough, a valve member movable in the valve body and obturating the compressed air flow path, aspirating means at one end of the compressed air flow path, the other end of the compressed air flow path opening out of the valve body remote from said aspirating means, a product containing means in the device and a product flow path through the device from the product containing means to the aspirating means. A hollow enclosure is provided at the end of the valve body over the said otherend of the compressed air flow path, and a piston is movable into the hollow enclosure toward the valve body. A conventional aerosol container having discharge valve means thereon opens into said hollow enclosure behind said piston, and said discharge means can be actuated to discharge propellant into the hollow enclosure to drive said piston to compress air in the hollow enclosure ahead of the piston. This piston engages the valve means after it has moved into the enclosure sufficiently far to build up the pressure of the air within-the enclosure in order to open the valve means to allow the compressed air to escape suddenly and flow along the compressed air flow path.

BRIEF DESCRIPTION OF THE FIGURES The invention will now be described in greater detail with reference to the accompanying drawing, in which:

FIG. I is a longitudinal sectional view of the device according to the invention with the parts in the rest or non-dispensing positions; FIGS. 2-4 are sections taken on lines 22, 3-3 and 4-4, respectively, of FIG. I and FIG. 5;

FIG. 5 is a view similar to FIG. 1 with the parts in the dispensing positions;

FIG. 6 is a perspective view of the device; and

FIG. 7 is a sectional view of a part of the device showing a modified form of seal member.

DETAILED DESCRIPTION OF THEFIGURES The device as shown inthe Figures comprises a valve body 10 which has a longitudinally extending recess 11 greater pressure than can be easily built up by the finger force of the user; Technical progress in the art would therefore be achieved if a dispenser of this type could be devised which could act on the piston with a force of compressed gas greater than that which can be produced by the finger of the user, yet the action of which could be initiated by simple finger pressure.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved fluid product dispenser of the type described abovewhich has the air compression means driven by a conventional aerosol propellant with a force of compressed gas greater than that which can be produced by simple finger pressure, but in which device the conventional propellant does not mix with the product to be dispensed.

It is a further object of the invention to provide an improved fluid product dispenserof the type described above in which the conventional propellant supply therein which opens out of the bottom of the valve body. A passage 12 extends from the upper end of the recess 11 and is intersected bya lateral opening 13 having a larger diameter portion 14. A Venturi nozzle insert 15 is positioned in the recess 13 so as to define a product supply chamber 16 around the nozzle insert. The recess 11 and the passage 12 form a compressed air flow path through the valve body to the nozzle insert 15. A product flow passage 17 extends upwardly from the product supply chamber 16 through the valve body 10.

Depending from the valve body 10 and integral therewith is a cylinder 18 defining a hollow enclosure 26 around the end of the compressed air flow path. Against the bottom of the valve body 10 within the inner end of the cylinder 18 is an apertured U-cup rubber seal member 19 having an aperture 20 in the center thereof. Above the seal member within the recess 11 is a valve member 21 which is urged toward the seal member I9 by a return spring 22 positioned in the recess 11. Spring 22 is sufficiently strong to resist the force of the valve member 21 through the opening 20 by air being compressed in cylinder 18. An unapertured piston 23 is slidably fitted into the cylinder 18 and has a sealing ring 30 therearound and an actuating pin 24 thereon which, when the piston reaches the inner end of the cylinder 18 extends through the aperture 20 in the seal member 9 and lifts the valve member 21 from the seal member 19. A return spring 25 is positioned between the piston 23 and the inner end of the cylinder 18, with the end at the inner end of the cylinder extending into the seal member 19. In the rest or non-dispensing condition for the device, the spring 25 exerts only sufficient force to hold the seal member 19 v at a position just slightly spaced from the inner end of cylinder 18 against the force of spring 22, as shown in FIG. 1. In addition the outside diameter of seal member 19 is slightly less than the inside diameter of cylinder 18. in the rest or non-dispensing positions of the parts as seen in FIG. 1, therefore, an air passage is provided through the nozzle insert 15, passage 12 and recess 11 and around the seal member 19 into the enclosure 26. During actuation and dispensing, this air passage is closed in a manner to be described hereinafter.

On the end of the valve body remote from the cylinder 18 is a product containing means 31 in the form ofa containier having a cap 32 fitted thereon and a slitted diaphragm 33 in the bottom thereof which covers a depression 34 into which the product flow path 17 opens. When compressed air flows through the nozzle insert 15, the reduced pressure is communicated to the depression 34, drawing the diaphragm 33 downwardly into the depression and opening the slit to allow product to be drawn through the slit and through the product flow path. The diaphragm 33 is held in place by a retaining ring 33a.

in the embodiment shown, a conventional aerosol propellant means is provided for driving the piston 23 into the hollow enclosure 26 of the cylinder 18. A housing 35 is provided around the valve body 10 and cylinder 18, within which the valve body and cylinder are slidable. The lower end of the housing 35 is closed by a bottom member 36, described in greater detail below, and within the bottom of the housing is positioned a conventional aerosol propellant cartridge 37 having a conventional spring loaded propellant valve 38 on the upper end thereof, which, in the preferred embodiment, is the type which opens to dispense a measured amount of propellant when it is depressed into the cartridge against the spring loading. The embodiment shown is for use in the upright position. If the device is designed to be used upside down, a dip tube 39 (shown in dotted lines) extends down into the cartridge from the valve means 38. A gasket or seal 40 is fixed in a groove 37a around the neck of the cartridge 37, which engages tightly in sealing fashion into an enlarged lower end of the cylinder 18 during actuation of the device. Fixed at the inner end ofthe enlarged lower end of cylinder 18 is an actuating member 41 having apertures 41a therein which is engaged with the valve 38 so that pressure from above will cause the valve to be depressed into the cartridge to release propellant. The member 41 also acts as a stop for the movement of the piston 23 out of the cylinder. An opening 42 is provided in housing 35 which is aligned with nozzle insert when the parts are in the operating positions as shown in FIG. 5.

Passage means is provided to discharge from the device the spent propellant which has been discharged into the space behind the piston 23 when the valve 38 is actuated. 1n the present embodiment, this means is a plurality of passages through the housing 35 extending back along the propellant cartridge 37 and out through the bottom member. A plurality of ribs 43 are provided around the inside of the lower portion of the housing 35 which holds the propellant cartridge 37 and defines passages 44 along with the inner surface of the housing 35 and the outer surface of the cartridge 37. The bottom member 36 is also formed with means defining passages. The bottom member is in the shape of an annular portion 36a having exterior threads 36b threaded into mating threads in the lower end of the housing 35. On the inner surface of the annular portion 36a, i.e. that portion facing the inside of the housing 35, is a plurality of ribs 36c spaced atintervals around the periphery of the annular portion 36a. The spaces 36e between the ribs 36c open upwardly into the interior of the housing 35. The central portion 36d forms a passageway from the spaces 36c out through the bottom of member 36. I

In operation, the device is preferably grasped in the hand with the index finger against the cap 32, and pressure is exerted by the finger on cap 32. The housing 35 and the valve body 10, cylinder 18 and product containing means 31 are first moved toward each other, the seal 40 engages in sealing engagement with cylinder 18, as shown in FIG. 5, and the actuating member 41 causes the aerosol valve 38 to be depressed, thus releasing a measured amount of aerosol propellantinto the space beneath the piston 23. The pressure of the propellant drives the piston'23 upwardly within the cylinder l8 and the air within the hollow enclosure 26 is compressed. At the start of compression, the spring 25 is slightly further compressed, driving the U-cup rubber seal member 19 tightly against the inner end of cylinder 18 and sealing off the recess 11 from the space 26. At the same time, the force of spring 22 presses the valve member 21 tightly against seal member 19. The force of spring 22 is sufficient to hold valve member 21 against seal member 19 against the force of the air being compressed in cylinder 18 until pin 24 on the piston engages the valve member 21 and opens it, as shown in FIG. 5. The compressed air is suddenly released through the compressed air flow path and is exhausted through the nozzle insert 15, thus aspirating product from the product containing means 31 through the product flow passage 17.

At this point, even if the user maintains the finger pressure, with the preferred form of valve 38, no further propellant will be discharged from the cartridge 37, and all that will happen will be that the piston will be held at the maximum compression position. No further air will be compressed, and no further product will be dispensed.

When the finger pressure is released, the spring force of the valve 38 will move the housing 35 and the valve body 10, cylinder 18 and product containing means 31 apart, thus breaking the sealing engagement of the ring 40 with the cylinder 18. The propellant within the space behind the piston 23 can then escape through the apertures 41a in the actuating member 41, past the seal 40, through the passages 44 and 36e and through the opening 36d. As the pressure of the propellant is reduced, the return springs 22 and 25 will return the valve member 21 and the piston 23 to their respective rest positions as shown in FIG. 1. This movement of the piston 23 will push any residual propellant through the passages. At this time, the combined force of spring 22 and vacuum in the space 26 will move seal member 19 down and air at atmospheric pressure will enter the device through the nozzle insert l5, passage 12, and recess 11 and will flow around the seal member into the cylinder space ahead of the piston 23.

If thedevice is designed to be used upside down, it is preferred to use some conventional means to positively hold the valve body and associated parts in the housing 35, such as lugs sliding in a groove in the valve body. Otherwise, the friction of O-ring 11 is sufficient to hold the parts together.

It will be seen that by selecting the desired pressure of the propellant in the cartridge 37, this pressure can be used to exert a force on piston 23 in order to move the piston to compress apredetermined volume of air in the hollow enclosure 26 to a desired pressure. The only force needed to achieve this pressure is that necessary to open the valve 38 on the cartridge 37, and this force is independent of the force necessary to achieve the desired compression. There is thus greater flexibility with respect to dimensioning of the cylinder and piston which makes possible greater compression or compression of larger amounts of air, since the limiting factor of finger force is eliminated, i.e. the compression is produced by the force of the propellant in the cartridge acting on the piston, not the tiger force. Moreover, the propellant is discharged out of the bottom of the device so that it does not come near the spray of dispensed product. Thus, the advantages of the use of the propellant are achieved, but none of the disadvantages are present.

By providing the type of valve in the propellant cartridge which dispenses only a measured amount of propellant, propellant is conserved, since the amount of propellant used is not dependent on the way in which the user actuates the device, but by the propellant cartridge valve.

It will be appreciated that with the type of cartridge which has the dip tube 39 extending into the propellant cartridge, the device can be used only with the cartridge in the upright position. Should it be desired to have the device so that it can be used upside down from the position shown in the drawings, a propellant cartridge without a dip tube can be used.

In order to increase the sealing effect of the sealing member when it is urged upwardly against the cylinder 18 by the propellant and'the piston return spring 25, a modified form of sealing member 19a can be provided as shown in FIG. 7, which has an outwardly flared skirt 1% which in its normal unstressed condition slides in light contact with the inside surface ofthe cylinder wall 18, but which when pressure is exerted from below by the propellant expands into tight sealing contact with the cylinder wall. When the propellant is vented from the space 26, air at atmospheric pressure coming around the sealing member 19a will flow easily past the skirt 19b to relieve the vacuum in the space 26.

What is claimed is:

l. A compressed air aspirating and propellant actuated dispenser for dispensing fluid products, comprising a valve assembly having an elongated valve body having a compressed air flow path therethrough, a valve member movable in said valve body and obturating the compressed air flow path. aspirating means at one end of the compressed air flow path, the other end of the compressed air flow path opening out of the valve body remote from said aspirating means, a product containing means in the device and said device having a product flow path therethrough from said product containing means to said aspirating means, said device having a hollow enclosure therein over the said other end of said compressed air flow path, an unapertured piston movable in said hollow enclosure toward said valve body and engagable with said valve member after it has moved into said hollow enclosure for actuating said valve member for opening said compressed air flow path, and an aerosol propellant cartridge having a spring loaded propellant cartridge dispensing valve mounted on said device for movement relative thereto for. opening said dispensing valve, said dispensing valve being directed into said hollow enclosure, whereby when said device is moved relative to said cartridge, propellant dispensed into said hollow enclosure drives said piston to compress air in said hollow enclosure ahead of the piston and the piston engages the valve member after it has moved into the enclosure sufficiently far to build up the pressure of the air within the enclosure in order to open the valve member to allow the compressed air to flow along the compressed air flow path.

2. A dispenser as claimed in claim 1 in which said device includes a housing positioned around said valve body within which the valve body is slidable, said cartridge being contained in said housing and having the propellant cartridge dispensing valve bearing against part of said valve body, whereby when the housing is moved relative to the valve body in a direction to urge said cartridge toward the valve body, the propellant cartridge dispensing valve is actuated to discharge propellant.

3. A dispenser as claimed in claim 2 in which said hollow enclosure is in said valve body and said valve body has an actuating member extending across the end of the hollow enclosure where it opens out of the valve body, said propellant cartridge dispensing valve being engaged with said actuating member for being opened when said cartridge is moved toward said valve body.

4. A dispenser as claimed in claim 2 in which said device has passage means therein from said hollow enclosure between said piston and said propellant cartridge to outside of said device for escape of spent propellant, and said device further has ,valve means in said passage means which closes said passage means when said propellant cartridge dispensing valve is open.

5. A dispenser as claimed in claim 4 in which said hollow enclosure is in said valve body and said valve body has an actuating member extending across the end of the hollow enclosure and covering less than all of the end of the hollow enclosure where it opens out of the valve body, said propellant cartridge dispensing valve being engaged with said actuating member for being opened when said cartridge is moved toward said valve body, said passage means extending along the outside of said cartridge in a direction away from said hollow enclosure and opening out of the bottom of said device, and said valve means in said passage means is a ring seal around said cartridge in sealing relationship therewith and sealingly engagable with the end of said valve body to seal said hollow enclosure when said cartridge is moved toward said valve body.

6. A dispenser as claimed in claim in which said ring seal is positioned on said cartridge to be in sealing engagement with said valve body when said propellant cartridge dispensing valve is fully actuated, whereby the spring action of the propellant cartridge dispensing valve when the force moving the cartridge toward the valve body is released breaks the sealing engagement between the ring seal and the valve body.

7. A dispenser claimed in claim Sin which said device includes a housing positioned around said valve body within which the valve body is slidable, said housing having ribs projecting into the housing for holding said cartridge, said ribs defining between them passages for escape of spent propellant, and said housing having openings in the bottom thereof through which said passages open out of the housing.

8. A dispenser as claimed in claim 7 in which said housing has a bottom member having an annular portion with ribs on the top thereof on which the cartridge rests, the spaces between the ribs constituting the openings for the spent propellant to escape through the bottom of the housing.

9. A dispenser as claimed in claim 1 in which said propellant cartridge dispensing valve is a valve of the type which dispenses only a measured amount of propellant.

10. A dispenser as claimed in claim 1 in which said hollow enclosure has a piston return spring therein urging said piston in a direction away from said valve body, and said valve body has a valve member return spring therein urging said valve member in a direction toward said piston, and a seal member in said enclosure between said piston return spring and said valve body and having an aperture therein and against which said valve member is urged for closing said aperture, and said piston return spring engaging said seal member and urging it toward said valve body, the relative forces of said springs when said dispenser has the parts in the non-dispensing rest positions holding said seal member slightly spaced from said valve body to leave an air return path around said seal member from said compressed air flow path into said hollow enclosure, whereby when the propellant drives the piston toward the valve member, the seal member is forced against the valve body to seal off the space therearound and said valve member is sealed against said seal member to seal the hollow enclosure completely from the compressed air flow path until the piston engages the valve member, and when propellant is vented from behind the piston, the seal member is moved away from the valve body to admit air to the hollow enclosure ahead of the piston. 

1. A compressed air aspirating and propellant actuated dispenser for dispensing fluid products, comprising a valve assembly having an elongated valve body having a compressed air flow path therethrough, a valve member movable in said valve body and obturating the compressed air flow path, aspirating means at one end of the compressed air flow path, the other end of the compressed air flow path opening out of the valve body remote from said aspirating means, a product containing means in the device and said device having a product flow path therethrough from said product containing means to said aspirating means, said device having a hollow enclosure therein over the said other end of said compressed air flow path, an unapertured piston movable in said hollow enclosure toward said valve body and engagable with said valve member after it has moved into said hollow enclosure for actuating said valve member for opening said compressed air flow path, and an aerosol propellant cartridge having a spring loaded propellant cartridge dispensing valve mounted on said device for movement relative thereto for opening said dispensing valve, said dispensing valve being directed into said hollow enclosure, whereby when said device is moved relative to said cartridge, propellant dispensed Into said hollow enclosure drives said piston to compress air in said hollow enclosure ahead of the piston and the piston engages the valve member after it has moved into the enclosure sufficiently far to build up the pressure of the air within the enclosure in order to open the valve member to allow the compressed air to flow along the compressed air flow path.
 2. A dispenser as claimed in claim 1 in which said device includes a housing positioned around said valve body within which the valve body is slidable, said cartridge being contained in said housing and having the propellant cartridge dispensing valve bearing against part of said valve body, whereby when the housing is moved relative to the valve body in a direction to urge said cartridge toward the valve body, the propellant cartridge dispensing valve is actuated to discharge propellant.
 3. A dispenser as claimed in claim 2 in which said hollow enclosure is in said valve body and said valve body has an actuating member extending across the end of the hollow enclosure where it opens out of the valve body, said propellant cartridge dispensing valve being engaged with said actuating member for being opened when said cartridge is moved toward said valve body.
 4. A dispenser as claimed in claim 2 in which said device has passage means therein from said hollow enclosure between said piston and said propellant cartridge to outside of said device for escape of spent propellant, and said device further has valve means in said passage means which closes said passage means when said propellant cartridge dispensing valve is open.
 5. A dispenser as claimed in claim 4 in which said hollow enclosure is in said valve body and said valve body has an actuating member extending across the end of the hollow enclosure and covering less than all of the end of the hollow enclosure where it opens out of the valve body, said propellant cartridge dispensing valve being engaged with said actuating member for being opened when said cartridge is moved toward said valve body, said passage means extending along the outside of said cartridge in a direction away from said hollow enclosure and opening out of the bottom of said device, and said valve means in said passage means is a ring seal around said cartridge in sealing relationship therewith and sealingly engagable with the end of said valve body to seal said hollow enclosure when said cartridge is moved toward said valve body.
 6. A dispenser as claimed in claim 5 in which said ring seal is positioned on said cartridge to be in sealing engagement with said valve body when said propellant cartridge dispensing valve is fully actuated, whereby the spring action of the propellant cartridge dispensing valve when the force moving the cartridge toward the valve body is released breaks the sealing engagement between the ring seal and the valve body.
 7. A dispenser as claimed in claim 5 in which said device includes a housing positioned around said valve body within which the valve body is slidable, said housing having ribs projecting into the housing for holding said cartridge, said ribs defining between them passages for escape of spent propellant, and said housing having openings in the bottom thereof through which said passages open out of the housing.
 8. A dispenser as claimed in claim 7 in which said housing has a bottom member having an annular portion with ribs on the top thereof on which the cartridge rests, the spaces between the ribs constituting the openings for the spent propellant to escape through the bottom of the housing.
 9. A dispenser as claimed in claim 1 in which said propellant cartridge dispensing valve is a valve of the type which dispenses only a measured amount of propellant.
 10. A dispenser as claimed in claim 1 in which said hollow enclosure has a piston return spring therein urging said piston in a direction away from said valve body, and said valve body has a valve member return spring therein urging said valve member in a direction toward said piSton, and a seal member in said enclosure between said piston return spring and said valve body and having an aperture therein and against which said valve member is urged for closing said aperture, and said piston return spring engaging said seal member and urging it toward said valve body, the relative forces of said springs when said dispenser has the parts in the non-dispensing rest positions holding said seal member slightly spaced from said valve body to leave an air return path around said seal member from said compressed air flow path into said hollow enclosure, whereby when the propellant drives the piston toward the valve member, the seal member is forced against the valve body to seal off the space therearound and said valve member is sealed against said seal member to seal the hollow enclosure completely from the compressed air flow path until the piston engages the valve member, and when propellant is vented from behind the piston, the seal member is moved away from the valve body to admit air to the hollow enclosure ahead of the piston. 